This article includes contributions from UK Health Security Agency ( UKHSA ) dosimetry specialists :

Nicky Gibbens ( PDS Manager )

Kinga Zmijewska ( PDS Technical Development Manager )

Matthew Simpson ( Data Manager , Internal Dosimetry )

External passive dosimetry Personal dosemeters are devices issued to employees to measure their external radiation dose and fall into two categories :

• Passive dosemeters which have no readout and must periodically be returned to a dosimetry service to retrospectively determine the average dose received .

• Personal Electronic Dosemeters ( PEDs ), which are discussed on page 6 of this magazine , give an immediate indication of dose rate , and also log the wearer ' s cumulative dose .

Whole body passive dosemeters measure both the “ deep ” whole body and “ shallow ” ( or “ surface ”) skin doses at specified depths below the body surface . There are also specialist dosemeters that measure doses to the extremities ( hands and feet ) and lens of the eye , as well as those that measure neutron and radon doses .

In the UK , most HSE-Approved Dosimetry Services use a passive thermoluminescent type of dosemeter ( TLD ) which measures both photon ( X-ray / gamma ) and beta radiation . The sensitive material in these dosemeters is lithium fluoride .

HSE Approved Dosimetry Services Employers must provide personal dose monitoring to classified workers through an HSE Approved Dosimetry Service ( ADS ). They must send their ADS accurate information about their employees and tell them when a classified person ceases to be classified or leaves their employment . Summaries of the dose information are held in HSE ' s Central Index of Dose Information ( CIDI ). Employees are entitled to request from the ADS copies of their own dose records and termination reports , including a complete dose history . Where an employer provides personal dose monitoring to non-classified workers , this does not have to be carried out by an ADS . However , employers must be able to demonstrate that measurements and assessments have been made to a satisfactory standard .

Thermoluminescent ( TL ) materials store the energy they absorb from ionising radiation until they are heated ( in this case to about 250 ° C ), when the energy is released as light . The amount of light released is proportional to the radiation dose .

The two sensitive elements in the dosemeter are positioned behind :

• a thick filter , to measure the “ whole body ” dose from strongly-penetrating radiation only ; and

• an open window , to measure the “ skin ” dose from both strongly- and weaklypenetrating radiation .

10 Radiation Protection Today www . srp-rpt . uk